The Stovebolt Site Forums The Parking Lot Big Bolts Shorting a big truck frame

Has anyone shorten a 3 ton frame and how much if so

I shortened a 2 ton COE from 158"in. down to 134"in. Seeing how these older truck frames taper as you get towards the rear, you just can't move the rear axle forward, & cut the overhang as you can later model trucks. What I did was made a cut just before the first cross member, then made the same cut just before the second cross member, then removed that 24"in. section, then welded back together. Didn't even have to do any drive shaft work. Went from three drive shafts, to two. Only had to splice my brake lines back together. Finished product was a factory correct 134"in. wheelbase.

I have a 2 ton and soon Ill be cutting out about 7 foot from the middle of mine so it will fit a fleet side long bed, the section I'm removing is bent I guess from overloading.

Here is the method I've always used and it is the accepted practice among professional truck upfitters and modifiers.
Make the cut to separate the frame as close to the center of two cross-members as practical to allow for the reinforcement inner angle or channel to fit. Be sure to cut it smoothly and free of jagged edges. Don't do this yourself unless your a practiced (good) torch man. Prop the frame up on a level floor so you can get the cab section and the rear axle sections pulled back together. Then grind the two pieces along the cut to about 30 degrees on all outer surfaces. Secure the two frame halves together by clamping a length of 5-6" steel channel to both top and along the sides. Your going to need a quantity of large C clamps for this. Do this to both sides of the frame and check/re-check all dimensions before going any further. Your cuts must be square.

Make any adjustments to the frame required to make the WB and the CA the same. If not the same the chassis will be out of square and it won't track or drive correctly. Then and only then does the welding begin. It is extremely important that you know the frame material your dealing with so that a proper weld and weld technique be employed. Most all of the the older chassis are not heat treated or high tensile material but not always so it is important to know. For nominal use that these old chassis will generally be used for it is acceptable to use a reinforcement angle (grade 50) that will fit inside the frame. Each end must be angled at 30 degrees and clamped inside the rails. A full penetration weld should be used on the two frame halves using the proper rod/wire etc. I always preferred the DC arc and a 70 series rod of 5/32 diameter depending on the original frame material and thickness for the older single frame trucks. Weld from bottom up. If you cannot weld well then get someone who can. I have also used a MIG process with satisfactory results. Make a clean fillett weld into the V you ground into the parts and make a full cut weld to re-join the halves. Grind the surface clean to smooth for appearance.

Now your ready to drill the holes for the bolts. Do NOT weld the inner channel to the original frame and do NOT weld anything to the flanges.
Make sure to use a minimum of 12" of overlap on the top of the inner channel and the bottom leg should be about 18" on either side of the cut. This is why it needs to be somewhat centered between the cross-members so there is sufficient room for the reinforcement angle. Then drill and bolt using an H pattern centered on the weld. Use 5/8" grade 5 bolts for this. Grade 8 is not necessary and adds nothing to a properly done job except expense. Use a minimum of 6 bolts at the cut and three at each end so it is a lot of hole drilling.

Have the driveshaft cut to the correct dimension and adjust the carrier bearing to the correct height so the driveline angle is correct. Take it to a drivleine shop for this and consult with them on the proper angle if you do not understand this aspect of the job. Make sure the shaft is installed in phase with it's mating parts or you'll get a tremendous vibration.

Join the cut brake line with a double flair union, secure it to the frame and bleed the brakes. Make the wiring connections in an accepted manner. (no scotch locks permitted!)

Clean and paint the surfaces. Chassis black is near the factory finish if it even had one. I used to pressure wash and remove any built up crud and grind away the usual scars and paint the frames on all my frame jobs. The customers loved it.

I have somewhat simplified the process here but it is not rocket science and can be done by an experienced mechanic/welder but is NOT a job for a beginner. You are supposed to THINK it through thoroughly before undertaking such a critical job as cutting you truck in two. Remember that your dealing with the backbone of your truck so it needs to be right or you'll regret it. If you decide to hire someone don't consider price as much as knowledge and experience.